Vibration damped sandwich systems



Dec. 15, 1970 Filed Nov. 18., 19681 H. OBERST ETAL VIBRATION DAMPED SANDWICH SYSTEMS 2 Sheets-Sheet FIG. 2Q

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ATTORNEYS United States Patent Office 3,547,758 Patented Dec. 15, 1970 3,547,758 VIBRATION DAMPED SANDWICH SYSTEMS Hermann Oberst, Hofheim, Taunus, Joachim Ebigt and Gnther Duve, Frankfurt am Main, and Alfred Schommer, Bad Soden, Taunus, Germany, assignors to Farbwerke Hoechst Aktiengesellschaft vormals Meister Lucius & Bruning, Frankfurt am Main, Germany, a corporation of Germany Filed Nov. 18, 1968, Ser. No. 776,529 Claims priority, application Germany, Dec. 6, 1967,

1,694,228 Int. Cl. B32lJ 15/08; CtlSf 19/02; E04b 1/99 U.S. Cl. 161-165 4 Claims ABSTRACT F THE DISCLOSURE A vibration damped sandwich system comprising two hard plates and interposed between the plates a vibration damping interlayer comprising a graft polymer of styrene and acrylonitrile on a copolymer of 30 to 40% by weight of vinyl acetate, 3040% by weight of Z-ethylhexyl acrylate, 30 to 10% by weight of dibutyl maleate and 5 to by weight of crotonic acid.

The present invention realtes to vibration damped sandwich systems having interlayers made of graft polymers of a mixture of styrene and acrylonitrile on vinyl acetate/ Z-ethylhexyl acrylate/dibutyl maleate/crotonic acid copolymers.

It is known from South African specification No. 5,269 that highly valuable vibrationed damping materials of a broad temperature band suitable for damping bending vibrations of metal Sheet constructions can be prepared by copolymerizing monomers whose homopolymers differ in their second order transition temperature by at least C. The above specification also reports that as vibration damping materials having a board temperature band there can be used, among others, predominantly amorphous copolymers of esters of alcohols with 4 to 12 carbon atoms with acrylic and maleic acid and vinyl esters of fatty acids with 2 to 3 carbon atoms, for example vinyl acetate/ 2-ethylhexyl acrylate and/ or dibutyl meleate copolymers.

It has now been found that graft polymers of a mixture of 66% by weight of styrene and 34% by weight of acrylonitrile on copolymers of vinyl acetate, suitable esters of unsaturated polymerizable carboxylic acids and an unsaturated copolymerizable acid, preferably crotonic acid, have outstanding damping properties, a large temperature range of damping and are thus especially suitable for the vibration damping of sandwich systems of hard plates, in particular metal sheets. Suitable esters are especially those of acrylic acid and maleic acid with alcohol components having 3 to 12 carbon atoms, preferably 2-ethylehexyl acrylate and dibutyl maleate. With these polymers, the vibration damping effect which critically depends on the weight proportion of the monomers, very broad damping curves can be obtained having very high maximum damping values. From the economical point of view they have the advantage of being rather cheap.

The graft polymers consisting of a mixture of 66% by weight of styrene and 34% by weight of acrylonitrile on copolymers of to 40% by weight of vinyl acetate, 30 to 40% by weight of 2-ethylhexyl acrylate, 30 to 10% by weight of dibutyl maleate and about 10% by Weight of crotonic acid are prepared by radical initiated polymerization at a temperature in the range of from about 60 to about C., by dissolving the copolymer in a mixture of 66% by weight of styrene and 34% of acrylonitrile containing a catalyst. Especially good results are obtained with graft polymers consisting of 40 to 80% by weight of a mixture of 66% by weight of styrene and 34% lby weight of acrylonitrile on 60% to 20% by weight of the copolymers specified above, for example a graft polymer of 50% by weight of a mixture of 66% by weight of styrene and 34% by weight of acrylnitrile on 50% by weight of the specied copolymer. As polymerization initiator tertiary butylhydroperoxide may be used.

The present invention provides sandwich systems of hard plates, in particular metal sheets, having vibration damping, self-adherent interlayers of graft polymers of a lmixture of 66% by weight of styrene and 34% by weight of acrylonitrile on vinyl acetate/2-ethylhexyl acrylate/ dibutyl maleate/crotonic acid copolymers, for which interlayers there are used graft polymers of 40 to 80% by weight of a mixture of 66% by weight of styrene and 34% by weight of acrylonitrile on 60 to 20% by weight of a copolymer consisting of 30 to 40% by weight of vinyl acetate, 30 to 40% by weight of 2-etliylhexyl acrylate, 30 to 10% by weight of dibutyl maleate and 5 to 10% by weight of crotonic acid.

FIGS. la and 1b of the accompanying drawings are plots against temperature of the loss factor dcomb to illustrate the superior eitciency of the novel systems. The curve in FIG. 1a shows the loss factor dcomb of a metal sheet arrangement of the invention as a function of temperature. For comparison, one of the most elective vibration damping materials known for metal sheet arrangements was used, namely a copolymer of 63% by weight of vinyl acetate and 37% by weight of dibutyl maleate containing as plasticizer 15% by weight of Z-ethylhexyl phthalate and 15% by weight of tricresyl phosphate, calculated on the mixture (curve FIG. 1b). The copolymer of curve 1b was a thermoplastic adhesive especially suitable for producing vibration damped metal sheet sandwich systems comprising two outer metal sheets and a self-adherent thermoplastic as damping interlayer. Systems of this type provide a damping etfect which is extremely high in its maximum and cannot be exceeded for physical reasons (cf. H. Oberst and A. Schommer, Kunststoie, volume 55, page 634 (1965), especially FIG. 9). In a symmetrical arrangement comprising two metal sheets, each having a thickness of 0.5 millimeter, and an interlayer 0.3 millimeter thick, the loss factor dcomb of the combined system, measured in the bending wave method (cf. for example H. Oberst, L. Bohn and F. Linhardt, Kunststoffe, volume 51, page 495 (1961)), almost reaches the value dumb of 1. The known metal sheet damping by one-side damping coatings which are applied by spraying, trowelling or bonding in the form of layers of so-called vibration damping materials show loss factors generally of less than dcomb: 0.2 with technically reasonable thicknesses or ratios of coating mass to plate mass of the combined system. With metal sheet sandwich systems which gain growing importance in recent times, it is possible to obtain damping values that are increased by a multiple, as shown by the present example, when the intel-layer material has the appropriate composition and thickness.

The temperature band width of the damping of the metal sheet sandwich system does not only depend on the viscoelastic properties of the interlayer and the steel sheets but also to a considerable extent of the geometry of the arrangement, i.e. on the ratio of the layer thicknesses (cf. loc. cit (1965), FIGIS. 8 to 10). With metal sheet sandwich systems the band width is advantageously dened as the range of the temperature interval within which the value dcom=-05 is exceeded. The damping of metal sheets which are not damped by additional vibration damping means in metal sheet constructions of various types corresponds to values dcombOl. The reference value dcomb of 0.05 thus means a considerable increase in the damping effect (by about 15 db (decibel)) as compared to the nil damping dcomb: 0.01.

In the curve shown in FIG. 1b the reference value dcomb of 0.05 is exceeded in the mainly interesting frequency range from 100 to 1,000 c.p.s. (HZ) at temperatures ranging from about 0 to 50 C. The temperature band Width thus corresponds to about 50 C. Sandwich systems of this type are suitable for many technical fields of application. By modifying the content of plasticizer, it is possible to shift the temperature band of a high damping effect to higher temperatures and thus to adapt the material to special technical uses, for example in machine units operating at elevated temperatures. This example of a metal sheet sandwich system comprising a self-adherent interlayer having optimum properties of a vibration damping material with a broad temperature band prepared by copolymerizing appropriate monomeric compounds has hitherto not been surpassed by other arrangements of similar kind and may be taken as standard for judging the acoustic eiciency of the system according to the invention.

FIGS. 1a and 1b show the temperature curves of the loss factor dcomb of metal sheet sandwich systems comprising steel sheets of a thickness of 0.5 millimeter each and damping interlayers of a thickness of 0.7 and 0.3 millimeter (FIG. 1b) for a frequency of 100 c.p.s. and 1,000 c.p.s.

The curves were measured with sandwich systems the interlayers of which consisted of (la) A graft polymer of 50% by Weight of a mixture of 66% by Weight of styrene and 34% by weight of acrylonitrile on 50% by weight of a copolymer of 35% by weight of vinyl acetate, 35% by weight of 2-ethylhexyl acrylate, 20% by weight of dibutyl maleate and by weight of crotonic acid (according to the invention),

(1b) a copolymer of 63% by weight of vinyl acetate and 37% of dibutyl maleate containing as plasticizer 15% by weight of Z-ethylhexyl phthalate and by weight of tricresyl phosphate, calculated on the mixture.

The arrangement 1a, whose monomer proportion lies in the optimum range has a very broad temperature band width with relatively high maximum damping values. VWith the arrangement la the center of damping is at about 30 to 45 C. with maximum damping values of about 0.5 to 0.8. The temperature band width is about 170 C. for 100 c.p.s. and about 110 C. for 1,000 c.p.s. In arrangement 1a, the slow decrease of the damping towards high temperatures at 100 c.p.s. and the extremely large width of the temperature band are especially favorable. Calculated on dcomb of 0.05 the excellent vibration damping properties are maintained at a temperature in the range of from about 7 C. to about 135 C. As compared with the standard system 1b, arrangement la has an appreciably broader temperature band width better damping properties above 30 C., so that arrangements of this type are suitable for quite a number of applications (for example in machines and appliances operated at normal and elevated temperatures). Owing to its content of 10% by weight of crotonic acid the graft polymer used in arrangement 1a can be cross-linked by reaction with a bifunctional or trifunctional compound (for example a Compound containing a plurality of: epoxide, isocyanate or similar groups), whereby the softening range and therewith the range of high damping can be noticeably shifted towards higher temperatures for special applications.

A special advantage of the vibration damping material of the present invention resides in the fact that it may be applied continuously during the mass production of the metal sheet sandwich systems.

For this purpose the vibration damping material can be applied (1) in the form of the nished graft polymer or (2) in the form of a solution of the specified copolymer in the mixture of styrene and acrylonitrile to be grafted containing the polymerization initiator and the graft polymer can be produced by a thermal treatment at a temperature in the range of from about 60 to about 180 C. of the sandwich system comprising the said solution as interlayer.

It is a thermoplastic adhesive which may be applied to the metal sheets by trowelling, brushing or pouring at elevated temperature. The sandwich system may then be advantageously cooled under pressure between rollers. Except for degreasing the metal sheets do not require a preliminary treatment and further adhesive. Owing to the content of the graft polymer of crotonic acid degreasing may even be dispensed with. The adhesion is very good.

The vibration damping material of the present invention has a good resistance to flow. The metal sheet sandwich system may, within broad limits, be processed as normal metal sheets, that is they may be creased, bent, shaped, welded and riveted. In this manner laminated systems are obtained having a damping height and temperature range of damping which makes them well suitable for many applications at normal and elevated temperatures.

Minor amounts of fillers, for example for improving the electric conductivity (improvement of resistance welding) may be incorporated in the vibration damping materials. In order not to affect the damping effect adversely it is advantageous to use less than 1% by Weight, preferably less than 0.5% by Weight of filler, calculated on the polymer. Suitable fillers, are, for example, heavy spar, silicic acid, graphite and soot.

The metal sheet sandwich system suitably has a total thickness in the range of from 1 to 6 millimeters. The interlayers may have a thickness of 0.1 to 1 millimeter, preferably 0.2 to 0.5 millimeter. A maximum damping effect is obtained with symmetrical laminated systems. With an equal weight, asymmetrical laminated systems have, however, a higher stiffness in exure and strength. Asymmetrical laminated systems are, therefore, preferred for those applications which require a high stregnth with respect to the weight. The ratio of the thicknesses of the outer plates or metal sheets is preferably within the range of from 1:1 to 1:4.

FIG. 2 of the accompanying drawings shows sandwich systems with symmetrical arrangement (a) and asymmetrical arrangement (b) in which the interlayer 2 is interposed between the two outer plates or metal sheets 1.

What is claimed is:

1. A vibration damped sandwich system comprising two hard plates and interposed between the plates a vibration damping interlayer comprising a graft polymer of 40 to 80% by weight of a mixture of 66% by weight of styrene and 34% by weight of acrylonitrile on 60 to 20% by weight of a copolymer of 30 to 40% by weight of vinyl acetate, 30-40% by weight of 2-ethylhexyl acrylate, 30 to 10% by weight of dibutyl maleate and 5 to 15% by weight of crotonic acid.

2. A vibration damped sandwich system as claimed in claim 1, wherein the hard plates are metal sheets.

3. A vibration damped sandwich system as claimed in claim 1, wherein the polymer of the interlayer contains up to 1% by weight of a filler, calculated on the copolymer.

4. A vibratoin damped sandwich system as claimed in claim 1, wherein the ratio of the thicknesses of the plates lies in the range of from 1:1 to 1:4.

References Cited UNITED STATES PATENTS Salyer. Albert et al. Burkus. Hardt et al. Salyer et a1.

6 3,414,638 1271968 Hardt et al. 3,433,724 3/ 1969 Gisur-vyette et al.

JOHN T. GOOLKASIAN, Primary Examiner 5 G. W. MOXON II, Assistant Examiner U.S. Cl. XR.

16T-21S; ISI-33; 260-785, 80.8, 80.81, 836, 837, 0 859, 881, 885 

